DE2939850A1 - METHOD AND DEVICE FOR IMPROVING THE SHARPNESS OF ELECTROSTATIC CHARGING IMAGES - Google Patents

Description

OR.-INQ. OIPL.-ING.M. SC. 011 "..- PHVS. SR DIPL-PHVS. DlPL-PHYS. Dft HÖGER - LEGAL RIGHTS - GRIESS3ACH - HAECKER PATENT LAWYERS IN SYüTlGARl

A 43 706 b Applicant: Savin Corporation

k - 177 Columbus and Stevens AV.

September 24, 197 9 Valhalla, New y _O rk 10

United States

Method and apparatus for improving the sharpness of electrostatic charge images

The invention relates to a method for improving the sharpness of an electrostatic developed with the aid of a liquid toner Charge image on a photoconductive surface and a device for carrying out the method.

In the production of graphic reproductions, particularly in electrophotographic copying, the resolution is and edge sharpness of a copied image is of great importance. The optical image with which a charged Photoconductor is exposed can be made quite sharp by using a high resolution lens system. The degree to which a photoconductor will acquire the electrostatic latent image obtained on that exposure depends on the composition and type of the photoconductive material used in the individual case. Given Reproduction accuracy of the photoconductor can lead to "smeared" or blurred electrostatic images. if either an out of focus original is used or if the out of focus is when the Photoconductor results. The resolution of the copier system can be expressed as a percentage with regard to the optics and the photoconductor Modulation of the transfer function can be specified.

The invention is based on the object of a method and a device for improving the sharpness of a developed electrostatic latent image on a

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Specify photoconductor.

According to the invention, this object is achieved in a method of the type described at the outset in that the developed charge image fully exposed.

To carry out the method according to the invention has a device particularly proven, which is characterized in that lighting devices for full-surface Illumination of the developed charge image are provided.

The decisive advantage of the method according to the invention is that the percent modulation is improved for all frequencies below an upper cutoff frequency can. This is particularly noticeable when a blurred original is to be reproduced. This advantage is achieved with very little additional technical effort.

In an earlier registration of the applicant (antical file number P 29 20 464.6) zvar is already a process bz <··. specified a device in which or in which also with a full-surface illumination of the bearing an image photoconductive surface of a copier is worked; according to the earlier application, this additional lighting is used however, to improve the effective response speed of a photoconductor to visible light. According to the invention on the other hand, if the resolution or sharpness of a picture is to be improved by the additional lighting, awake is already fully developed using a liquid toner or developer, with a liquid

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Toner or developer is to be understood as a liquid in the toner particles are dispersed, which in the already developed, often later still on a sheet-shaped OSger to be transferred image of the original to be copied remain mobile until the carrier liquid has evaporated.

Earlier developments in the field of interest here, for example in US Pat. Nos. 2 7 56 67 6, 3 907 4 23, 3,912,387 and 3,994,723 also failed to develop the new method of improvement stimulate the sharpness of the reproduced eggs. In detail the proposal has been made in US Pat. No. 2,756,676, with only a single exposure process using a Originals to create multiple copies of an image produced in the process. In the known method, the photoconductor recharged after each transfer of a developed image, whereupon the recharged charge image is amplified by illuminating it. The patent mentioned does not contain any suggestion that the sharpness of the developed image improves before it is transmitted can be. In particular, according to the cited patent, a toner is used in the form of a dry powder, so that no moving toner particles are present after development, as they are according to the invention for the Need to improve the sharpness of the image. U.S. Patent 3,907,423 describes a copier with a counter rotating Roller, which serves to remove excess liquid after developing the latent electrostatic image from the Remove the photoconductor. A suggestion in the direction of the invention can also not be found in this patent specification. Finally, US Patents 3,912,387 and 3,994,723 describe ways of determining underexposed background

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areas and for discharging the same by illumination before developing a latent electrostatic charge image. According to the invention, on the other hand, the entire area of the photoconductor must be illuminated after the latent electrostatic has been developed Charge image take place.

Details and advantages of the invention are explained in more detail below with reference to drawings. Show it:

1 shows a schematic representation of the potentials on a photoconductive surface after exposure, wherein the distribution of the toner after the development of the electrostatic latent image in full Lines is shown while the potentials on the photoconductive surface according to the invention made full-surface lighting with dashed Lines are shown.

2 shows a schematic representation of a preferred embodiment a copier for carrying out the method according to the invention.

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Description of a preferred embodiment:

In general, a common electrophotographic one is used in the present invention Copier used in which a photoconductive surface is charged and then the light-dark image of an original is exposed to form an electrostatic latent image on the photoconductive surface. This picture will be then developed by one of the known methods using a liquid developer, which toner particles in a liquid carrier. The developed image consists initially of deposited toner particles that are deposited on the photoconductive surface are still movable. Such a developed image can in many cases be on the edges of the loaded Image areas have a certain degree of blurring, which can be attributed to a "smeared" original or to aberrations of the optical System is due. After the electrostatic image has developed, but before it is transferred to a sheet-shaped carrier - if such a transfer takes place carbon black - is the photoconductive surface with the electrostatic developed using a liquid developer Charge image completely exposed to further discharge background areas of the photoconductive surface. Since the density of the toner deposit in the areas adjoining the areas of maximum density is comparable is weak, some of the light penetrates the areas that are weakly covered with toner particles, making the photoconductive Surface is further discharged in these areas. The reduction in the electrostatic charge releases the toner particles that were previously only slightly fixed and still mobile free. These released toner particles are then attracted to more charged areas, leaving them blurred Edges are omitted and a sharp image is obtained, which gives the impression of better resolution.

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The device for carrying out the method according to the invention has a light source for full-surface exposure, which in the path of the moving photoconductive surface which carries a developed electrostatic image. The full-area illumination of the photoconductive surface takes place, before the developed image is transferred to a sheet support, if such transfer takes place. if If a sheet coated with a photoconductive material is used, there is no transfer to a sheet-shaped one Carrier material instead.

If one now looks in detail at FIG. 1 of the drawing, one recognizes that there the potential of the photoconductive surface for an unexposed area and exposed areas is plotted on a logarithmic scale, with simultaneously the distribution of the toner after the development of a latent electrostatic charge image is indicated. Of the The course of the potential is shown in 4n solid lines. Furthermore, the course of the potential of the photoconductive surface after the full-surface exposure of the developed Toner image shown in dashed lines. In detail, a picture area 1OO can be seen in FIG. 1, where the photoconductive Surface is charged to 600 V. ll background areas 102, may be adjacent to the unexposed image area 1OO, are, however, discharged to a potential of 50 V. Furthermore, in the image area 100 there is a deposited layer of Toner particles 104 shown. There are also transition areas between the image area 100 and the background areas 102 106, which normally lead to blurred edges of the image areas and in which there is a weak layer of toner 1OB results. When a photoconductive surface carrying a developed toner image for which the above

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explained relationships apply, is fully exposed, then the potential in the background areas is further reduced, for example to 20 V, as indicated by the dashed lines Lines 110 is indicated. The weak toner layers 108 disappear due to the fact that the Toner particles come free from the transition areas 106 during the further discharge. The released toner particles migrate now to the charged image area 100, which they developed due to their mobility in the with a liquid developer Charge image is possible.

Fig. 2 of the drawing shows an apparatus for performing the method according to the invention or a copier with a Metal drum 10, which has a photoconductive layer or surface 12, for example made of selenium. The metal drum is carried by disks 14 which have a central opening in the area of which they are wedged with a shaft 16 in a rotationally fixed manner are. The shaft 16, which can be grounded, is driven by means of suitable drive devices, so that the drum 10 with the direction of rotation indicated by an arrow - counterclockwise - rotates. It's a charge serving corona discharge device 18 is provided, with the help of which the surface of a photoconductor, for example the selenium surface 12 of the drum 10, to a voltage between and 1000 V can be charged. To do this, will the corona discharge device 18 is fed with a positive potential between 50OO and 6000V. The corona discharge device 18, ensures an ionization of the surrounding atmosphere, so that there is a uniform positive on the selenium surface Charge results, (it is understood that when using zinc oxide as a photoconductor a negative charge from electrons is used j after passing the corona discharge device 18 passes through the photoconductive surface 12 a

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Exposure station 20. There, with the help of projection optics, which is indicated schematically by a lens 22, an image of an original to be copied is projected onto the photoconductive surface 12.

After this exposure of the photoconductive surface, the electrostatic latent image using a developed liquid developer, preferably working with a toner system as it is in US Pat. No. 3,892,481 is described, according to which a tank 46 is used, to which the liquid developer or toner 48 in one Circuit is fed via a line 52 which is connected to a storage tank (not shown) and from which the liquid toner flows through a line 50 to the storage tank. A developer electrode 54 is provided in the tank 46, whose potential is regulated so that any residual charges in the background areas of the photoconductive surface be compensated. The bias voltage for the developer electrode 54 is so regulated that it is slightly above the The potential of the background areas 102 is. In this way it is achieved that the background areas do not contain any toner particles capture, as these migrate to the developer electrode.

After the charge image has been developed with toner particles suspended in a liquid, the excess developer liquid is wiped off the developed image with the aid of a counter-rotating roller 56, as described in US Pat. No. 3,907,423. The counter-rotating roller 56 is provided with a scraper 58 and is otherwise arranged _f and driven at such a speed as is described in the aforementioned US-PS.

In the known copying processes in which the developed Image is transferred to a sheet-shaped carrier

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the image is now ready for transfer to the sheet-like carrier, in particular to plain paper. According to the invention, however, an incandescent lamp 142 is arranged behind the developer station, based on the direction of rotation of the drum 10, which is arranged before the image transfer required in the embodiment and the developed image with light flooded, whereby the potential of the background areas is reduced, so that the only loosely held toner particles in the transition areas are released and to the higher charged image areas of the charge image can migrate. The full-surface illumination results in sharper contours and a significantly better resolution.

According to FIG. 2, after the exposure to obtain a sharper image, a sheet of normal paper 60 is fed to the circumference of the drum with the aid of feed rollers 62, which is transported under a corona discharge device 66 serving for image transfer to a roller 64. The corona discharge device 66 generates a high positive charge on the rear side of the paper sheet 60. Because of this charge, the toner particles are drawn from the image areas of the drum surface onto the paper. if a sticky toner is used, the image transfer can be achieved by applying pressure between roller 64 and the drum surface 12 take place. A stripper 68 ensures that the paper is lifted from the drum surface and that the leading edge 70 of the paper, which now carries the image, a drying device and finally a Collection basket can be fed. Behind the transfer station, a cleaning roller 72 cleans the drum of residual

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toner particles, and cleaning the drum surface is finally perfected by a scraper blade 74.

As is clear from FIGS. 1 and 2, according to the invention an incandescent lamp 142 or other suitable light source for a full area illumination adjacent to the photoconductive Surface 12 bearing a developed image which has not yet been transferred, i.e. H. between the Developer station and the transfer station. The light bulb serves to cover it with a weak layer of toner To discharge edge and transition areas even further and the only loosely held toner particles at the edge areas to release, which would otherwise lead to blurred contours.

It goes without saying that the invention is in no way limited to the above described embodiment is limited. Based on the embodiment described are the Rather, a person skilled in the art has numerous possibilities for changes and / or additions to bids without him doing the basic idea the invention would have to leave.

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Claims (1)

OH. -INTO THE. DIPL-ING. M. SC. DIPL.-PHYS. OR. DIPL-PHYS. DIPL-PHYS. THERE. HÖGER - LEGAL LAW - GRIESS3ACH - HAECKER BOEHME PATENT ANWiLlL IN 5, '. UTIGARI A 43 706 b Applicant: Savin Corporation k - 177 Columbus and Stevens AV September 24, 197 9 Valhalla, New York 10 United States Claims 1. Method of improving the sharpness of a using of a liquid toner developed an electrostatic charge image on a photoconductive surface, thereby characterized in that the developed charge image is exposed over the entire area. 2. Statute of limitations according to claim 1, in which one is initially on a uniformly charged photoelectric surface by exposure to the image of an original, a latent electrostatic charge image is generated, in which one the latent charge image is then developed into a visible charge image with a liquid toner and in the case of the the developed charge image is transferred to a sheet-shaped carrier, characterized in that the full-surface exposure before the transfer of the visible charge image onto the sheet-like carrier performs. 3. Device for performing the method according to claim 1, characterized in that lighting devices to the complete dampening of the developed Charge pattern are provided. 4. Apparatus according to claim 3, characterized in that that / \ ndrive equipment to bring about a return 030021/0613 _ ₂ _ A 43 706 b k - 177 September 24, 1979 - & - 2933850 relative movement between the lighting devices and the photoelectric surface carrying the charge image are provided. 5. Apparatus for improving the sharpness of a developed, electrophotographically generated image, with a Photoconductor, with drive devices for guiding the photoconductor past a charging station for electrostatic purposes Charging of the surface of the photoconductor to then lead the photoconductor past an exposure station, on which the charged photoconductive surface is a light / shadow image of a to be reproduced The original is exposed, creating a latent electrostatic charge image of the original, and to then lead the photoconductor past a development station where the electrostatic. Charge image is developed with a liquid toner to produce a visible developed charge image, for performing the method according to claim 1, characterized characterized in that lighting devices for full-surface exposure of the developed charge image are provided, and that drive devices for guiding the electrostatic charge image past are provided on the lighting equipment. 6. Copier for the electrophotographic production of copies of an original with a photoconductor with charging devices for charging the photoconductor, with exposure devices for exposing the charged photoconductor, with a light / shadow image of the template to be copied - 3 030021/0613 A 43 706 b k - 177 September 24, 1979 - - "S" - able to form an electrostatic latent image with developing devices for developing the latent electrostatic charge image with the help of a liquid developer, with transfer devices for transferring the developed charge image to a sheet-shaped carrier and with drive devices for successively leading the photoconductor past the charging devices, the exposure devices, the development facilities and the transfer facilities for carrying out the process Claim 1, characterized in that between the development devices and the transfer devices Illumination devices for full-area exposure of the developed electrostatic charge image are provided on the photoconductor. 7. Copier for the electrophotographic production of copies of an original with a photoconductor, with a Charging station for electrostatic charging of the photoconductor, with more of an exposure station for exposure of the charged photoconductor with a light / shadow image the original to be copied to form a latent electrostatic charge image the photoconductor, with a developer station for developing the latent charge image into a visible one electrostatic charge image with the aid of a liquid toner and with devices for generating it a relative movement between the photoconductor and the charging station, the exposure station and the development station, to carry out the procedure? according to claim 1, characterized in that a lighting station is provided on which the developed electrostatic charge image is fully exposed to light is used to increase the sharpness of the visible charge 030021/0613 A 43 706 b k - 177 September 24, 1979 des to increase and that drive devices to lead past of the visible, developed electrostatic charge image on the photoconductor are provided at this lighting station. 030021/0613